Exhaust purification system of internal combustion engine

ABSTRACT

A particulate filter for trapping particulate filter which is contained in exhaust gas is arranged in an engine exhaust passage. The particulate filter is provided with exhaust gas inflow passages and exhaust gas outflow passages which are alternately arranged via porous partition walls. Movement promoting control is performed to promote movement of the ash which deposits on the inner circumferences of the exhaust gas inflow passages to the rear parts of the exhaust gas inflow passages. The pressure loss of the particulate filter is detected. When the detected pressure loss is larger than a predetermined upper limit value, PM removal control is performed to remove the particulate matter from the particulate filter.

TECHNICAL FIELD

The present invention relates to an exhaust purification system of aninternal combustion engine.

BACKGROUND ART

Known in the art is an internal combustion engine which arranges aparticulate filter for trapping particulate matter which is contained inexhaust gas in an engine exhaust passage. This particulate filter isprovided with exhaust gas inflow passages and exhaust gas outflowpassages which are arranged alternately via porous partition walls. As aresult, exhaust gas first flows into the exhaust gas inflow passages,then passes through the partition walls and flows out into the exhaustgas outflow passages. Therefore, the particulate matter which iscontained in the exhaust gas is trapped inside the partition walls or onthe surfaces of the partition walls which form the inner circumferenceof the exhaust gas inflow passages.

As the amount of particulate matter which deposits on the particulatefilter becomes greater, the pressure loss of the particulate filterbecomes greater. If the pressure loss of the particulate filter becomesgreater, the engine output is liable to fall. Therefore, known in theart is an exhaust purification system of an internal combustion enginewhich detects the pressure loss of the particulate filter and, when thepressure loss exceeds an upper limit value, performs PM removal controlwhich removes the particulate matter from the particulate filter (seePLT 1).

CITATIONS LIST Patent Literature

PLT 1: Japanese Patent Publication No. 2005-76462A

SUMMARY OF INVENTION Technical Problem

In this regard, exhaust gas contains noncombustible ingredients called“ash”. This ash is trapped together with the particulate matter by theparticulate filter. In this regard, even if PM removal control isperformed, the ash will not burn or will not vaporize. That is, the ashis not removed from the particulate filter, but remains on theparticulate filter. As a result, the pressure loss of the particulatefilter becomes larger by the amount of ash which is deposited on theparticulate filter. For this reason, if performing PM removal control bythe pressure loss of the particulate filter exceeding the upper limitvalue, PM removal control is liable to be performed regardless of theamount of the particulate filter which is deposited on the particulatefilter being relatively small. That is, the timing of execution of PMremoval control is liable to be advanced from the optimum timing.Therefore, PM removal control is liable to be unpreferably performedfrequently and the energy which is consumed for PM removal control isliable to increase.

Solution to Problem

According to the present invention, there is provided an exhaustpurification system of an internal combustion engine which is providedwith a particulate filter for trapping particulate matter which iscontained in exhaust gas inside an engine exhaust passage, whichparticulate filter is provided with exhaust gas inflow passages andexhaust gas outflow passages which are alternately arranged throughporous partition walls, characterized in that the system comprises: amovement promoting means or a movement promoter for promoting movementof ash which deposited on inner circumferences of the exhaust gas inflowpassages to rear parts of the exhaust gas inflow passages; a detectingmeans or a detector for detecting pressure loss of the particulatefilter; and a PM removing means or a PM remover for performing PMremoval control for removing particulate matter from the particulatefilter when the detected pressure loss is greater than a predeterminedupper limit value.

Preferably, the movement promoting means judges if the amount of ashwhich has deposited on the inner circumferences of the exhaust gasinflow passages is greater than a predetermined upper limit amount andperforms movement promoting control when it is judged that the amount ofash is greater than the predetermined upper limit amount.

Preferably, the movement promoting means supplies a liquid to theparticulate filter to perform the movement promoting control. Morepreferably, the liquid is comprised of at least one of water, an aqueoussolution, and a liquid fuel. Still more preferably, at least one of anengine intake passage, engine exhaust passage upstream of theparticulate filter, and exhaust gas recirculation passage which connectsthe engine intake passage and engine exhaust passage with each other isformed with a condensed water storage part which stores condensed waterwhich is generated at the internal combustion engine, and the movementpromoting means supplies condensed water which was stored in thecondensed water storage part to the particulate filter, to perform themovement promoting control. Still more preferably, the system furthercomprises an NOx reducing catalyst which is arranged inside theparticulate filter or in the engine exhaust passage downstream of theparticulate filter; a reducing agent addition valve which secondarilyadds a liquid reducing agent into the engine exhaust passage upstream ofthe particulate filter; and a NOx reducing means or a NOx reducer foradding the liquid reducing agent from the reducing agent addition valvewith a NOx reduction addition pressure and NOx reduction addition timefor reducing the NOx, and that the movement promoting means adds liquidreducing agent from the reducing agent addition valve with an additionpressure which is lower than the NOx reduction addition pressure or withan addition time which is longer than the NOx reduction addition time,to perform the movement promoting control.

Preferably, the movement promoting means makes the pressure inside ofthe particulate filter pulsate, to perform the movement promotingcontrol.

Preferably, the movement promoting means makes the particulate filtervibrate, to perform the movement promoting control.

Preferably, the movement promoting means makes the temperature of theparticulate filter rise to a temperature higher than that at the time ofPM removal control, to perform the movement promoting control.

Preferably, the movement promoting means feeds a liquid to theparticulate filter and makes the liquid solidify, to perform themovement promoting control.

Advantageous Effects of Invention

PM removal control can be performed at the optimum timing.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a schematic view of a cooling device.

FIG. 3A is a front view of a particulate filter.

FIG. 3B is a side cross-sectional view of a particulate filter.

FIG. 4 is a time chart which explains PM removal control.

FIG. 5A is a map which shows an amount of increase.

FIG. 5B is a map which shows an amount of decrease.

FIG. 6 is a flow chart which shows a routine for executing PM removalcontrol.

FIG. 7 is a flow chart which shows a routine for calculating an amountof deposited particulate matter QPM.

FIG. 8A is a graph which shows a relationship between a pressuredifference PD and an amount of deposited particulate matter QPM.

FIG. 8B is a graph which shows a relationship between a pressuredifference PD and an amount of deposited particulate matter QPM.

FIG. 8C is a graph which shows a relationship between a pressuredifference PD and an amount of deposited particulate matter QPM.

FIG. 8D is a graph which shows a relationship between a pressuredifference PD and an amount of deposited particulate matter QPM.

FIG. 9A is a partial enlarged cross-sectional view of a particulatefilter which shows ash which is deposited on an inner circumference ofan exhaust gas inflow passage.

FIG. 9B is a partial enlarged cross-sectional view which shows ash whichis deposited at a rear part of an exhaust gas inflow passage.

FIG. 10 is a time chart which explains movement promoting control.

FIG. 11A is a graph which explains a difference between intercepts oftwo asymptotes.

FIG. 11B is a graph which explains a difference between intercepts oftwo asymptotes.

FIG. 12 is a flow chart which shows a routine for executing engine startcontrol.

FIG. 13 is a flow chart which shows a routine for executing movementpromoting control.

FIG. 14 is a flow chart which shows a routine for executing idlingcontrol.

FIG. 15 is a flow chart which shows a routine for calculating a ratio R.

FIG. 16 is a graph which explains another embodiment of the ratio R.

FIG. 17A is a view which shows another embodiment of a condensed waterstorage part.

FIG. 17B is a view which shows another embodiment of a condensed waterstorage part.

FIG. 17C is a view which shows another embodiment of a condensed waterstorage part.

FIG. 18 is an overview of an internal combustion engine which showsanother embodiment of the present invention.

FIG. 19 is a time chart which explains movement promoting control of theembodiment which is shown in FIG. 18.

FIG. 20 is a flow chart which shows a routine for executing the movementpromoting control which is shown in FIG. 19.

FIG. 21 is an overview of an internal combustion engine which showsstill another embodiment according to the present invention.

FIG. 22 is a time chart which explains movement promoting control of theembodiment which is shown in FIG. 21.

FIG. 23 is a flow chart which shows a routine for executing the movementpromoting control which is shown in FIG. 22.

FIG. 24A is an overview of an internal combustion engine which showsstill another embodiment according to the present invention.

FIG. 24B is an overview of an internal combustion engine which showsstill another embodiment according to the present invention.

FIG. 24C is an overview of an internal combustion engine which showsstill another embodiment according to the present invention.

FIG. 25 is an overview of an internal combustion engine which showsstill another embodiment according to the present invention.

FIG. 26 is a time chart which explains movement promoting control of theembodiment which is shown in FIG. 25.

FIG. 27 is a flow chart which shows a routine for executing the movementpromoting control which is shown in FIG. 26.

FIG. 28 is an overview of an internal combustion engine which showsstill another embodiment according to the present invention.

FIG. 29 is a time chart which explains movement promoting control of theembodiment which is shown in FIG. 28.

FIG. 30 is a flow chart which shows a routine for executing the movementpromoting control which is shown in FIG. 29.

FIG. 31 is a time chart which explains still another embodimentaccording to the present invention.

FIG. 32 is a flow chart which shows a routine for executing the exhaustpurification control which is shown in FIG. 31.

FIG. 33 is a flow chart which shows a routine for executing the movementpromoting control which is shown in FIG. 31.

FIG. 34 is a time chart which explains still another embodimentaccording to the present invention.

FIG. 35 is a flow chart which shows a routine for executing engine stopcontrol which is shown in FIG. 34.

FIG. 36 is a flow chart which shows a routine for executing engine startcontrol which is shown in FIG. 34.

FIG. 37 is a flow chart which shows a routine for executing movementpromoting control during stop which is shown in FIG. 34.

FIG. 38 is a flow chart which shows a routine for executing movementpromoting control during start which is shown in FIG. 34.

FIG. 39 is an overview of an internal combustion engine which showsstill another embodiment according to the present invention.

FIG. 40 is a time chart which explains movement promoting control of theembodiment which is shown in FIG. 39.

FIG. 41 is a flow chart which shows a routine for executing movementpromoting control during stop which is shown in FIG. 40.

DESCRIPTION OF EMBODIMENTS

Referring to FIG. 1, 1 indicates a body of a compression ignition-typeinternal combustion engine, 2 a combustion chamber of each cylinder, 3an electronically controlled fuel injector which injects fuel into acombustion chamber 2, 4 an intake manifold, and 5 an exhaust manifold.The intake manifold 4 is connected through an intake duct 6 to an outletof a compressor 7 c of an exhaust turbocharger 7, while an inlet of thecompressor 7 c is connected through an air flowmeter 8 to an air cleaner9. Inside the intake duct 6, an electrically controlled throttle valve10 is arranged.

Furthermore, around the intake duct 6, a cooling device 11 is arrangedfor cooling the intake air which flows through the inside of the intakeduct 6. On the other hand, the exhaust manifold 5 is connected to aninlet of an exhaust turbine 7 t of the exhaust turbocharger 7, while anoutlet of the exhaust turbine 7 t is connected to an exhaustpost-treatment device 20.

The exhaust manifold 5 and the intake manifold 4 are connected to eachother through an exhaust gas recirculation (hereinafter referred to as“EGR”) passage 12. Inside the EGR passage 12, an electrically controlledEGR control valve 13 is arranged. Further, in the EGR passage 12, acooling device 14 is arranged for cooling the EGR gas which flowsthrough the inside of the EGR passage 12. On the other hand, each fuelinjector 3 is connected through a fuel runner 15 to a common rail 16.The inside of this common rail 16 is supplied with fuel from anelectronically controlled variable discharge fuel pump 17. The fuelwhich is supplied to the inside of the common rail 16 is suppliedthrough each fuel runner 15 to a fuel injector 3. In the embodimentwhich is shown in FIG. 1, this fuel is comprised of diesel oil. Inanother embodiment, the internal combustion engine is comprised of aspark ignition type internal combustion engine at which fuel is burnedwith a lean air-fuel ratio. In this case, the fuel is comprised ofgasoline.

The exhaust post-treatment device 20 is provided with an exhaust pipe 21which is connected to the outlet of the exhaust turbine 7 t, a catalyticconverter 22 which is connected to the exhaust pipe 21, and an exhaustpipe 23 which is connected to the catalytic converter 22. Inside of thecatalytic converter 22, a wall flow type of particulate filter 24 isarranged.

The catalytic converter 22 is provided with a temperature sensor 25 fordetecting the temperature of the particulate filter 24. In anotherembodiment, a temperature sensor is arranged in the exhaust pipe 21 todetect the temperature of the exhaust gas which flows into theparticulate filter 24. Furthermore, in another embodiment, a temperaturesensor for detecting the temperature of the exhaust gas which flows outfrom the particulate filter 24 is arranged in the exhaust pipe 23. Thetemperatures of the exhaust gas express the temperature of theparticulate filter 24.

The catalytic converter 22 is further provided with a pressure losssensor 26 for detecting the pressure loss of the particulate filter 24.In the example which is shown in FIG. 1, the pressure loss sensor 26 iscomprised of a pressure difference sensor for detecting the pressuredifference upstream and downstream of the particulate filter 24. Inanother embodiment, the pressure loss sensor 26 is comprised of a sensorwhich is attached to the exhaust pipe 21 and detects the engine backpressure.

On the other hand, the exhaust manifold 5 is provided with a fueladdition valve 27. This fuel addition valve 27 is supplied with fuelfrom the common rail 16. From the fuel addition valve 27, fuel is addedinside of the exhaust manifold 5. In another embodiment, the fueladdition valve 27 is arranged in the exhaust pipe 21.

FIG. 2 shows a cooling device 14 which is provided in the EGR passage12. The cooling device 14 is provided with a main passage 14 a which isconnected to the EGR passage 12, a cooler 14 b which is arranged aroundthe main passage 14 a, a bypass passage 14 c which branches from themain passage 14 a upstream of the cooler 14 b and returns to the mainpassage 14 a downstream of the cooler 14 b, and a bypass control valve14 d which selectively guides EGR gas to one of the main passage 14 aand bypass passage 14 c. When the EGR gas should be cooled, the bypasscontrol valve 14 d is controlled to the cooling position which is shownby the solid line in FIG. 2, therefore the EGR gas is guided to thecooler 14 b. As opposed to this, when the EGR gas is not to be cooledsuch as at the time of cold operation, the bypass control valve 14 d iscontrolled to the bypass position which is shown by the broken line inFIG. 2, therefore the EGR gas bypasses the cooler 14 b. Furthermore, thebypass passage 14 c is provided with a condensed water storage part 14 efor storing condensed water which is formed in the EGR passage 12 andthe cooling device 14. In the embodiment which is shown in FIG. 2, thecondensed water storage part 14 e is comprised of a recessed part whichis formed at the bottom surface of the bypass passage 14 c.

Referring again to FIG. 1, the electronic control unit 30 is comprisedof a digital computer which is provided with components which areconnected with each other by a bidirectional bus 31 such as a ROM (readonly memory) 32, RAM (random access memory) 33, CPU (microprocessor) 34,input port 35, and output port 36. The output signals of the airflowmeter 8, temperature sensor 25, and pressure difference sensor 26are input through respectively corresponding AD converters 37 to theinput port 35. Further, the accelerator pedal 39 is connected to a loadsensor 40 which generates an output voltage which is proportional to theamount of depression L of the accelerator pedal 39. The output voltageof the load sensor 40 is input through a corresponding AD converter 37to the input port 35. The engine body 1 has a water temperature sensor41 for detecting the engine cooling water temperature and an oiltemperature sensor 42 for detecting the engine lubrication oiltemperature attached to it. The output voltages of these sensors 41 and42 are input through the corresponding AD converters 37 to the inputport 35. Furthermore, the input port 35 is connected to a crank anglesensor 43 which generates an output pulse each time the crankshaftrotates by for example 15°. At the CPU 34, the output pulse from thecrank angle sensor 43 is used as the basis to calculate the engine speedNe. The input port 35 further receives as input the signals which showif the ignition switch 44 and the starter switch 45 are on or off. Whenthe starter switch 45 is on, the starter motor 46 is actuated. On theother hand, the output port 36 is connected through corresponding drivecircuits 38 to the fuel injectors 3, throttle valve 10 drive device, EGRcontrol valve 13, bypass control valve 14 d, fuel pump 17, fuel additionvalve 27, and starter motor 46.

FIG. 3A and FIG. 3B show the structure of the wall flow type particulatefilter 24. Note that, FIG. 3A shows a front view of the particulatefilter 24, while FIG. 3B shows a side cross-sectional view of theparticulate filter 24. As shown in FIG. 3A and FIG. 3B, the particulatefilter 24 forms a honeycomb structure which is provided with a pluralityof exhaust flow passages 71 i, 710 which extend in parallel with eachother and partition walls 72 which separate these exhaust flow passages71 i, 71 o. In the embodiment which is shown in FIG. 3A, the exhaustflow passages 71 i, 71 o are comprised of exhaust gas inflow passages 71i which have upstream ends which are opened and have downstream endswhich are closed by plugs 73 d and exhaust gas outflow passages 710which have upstream ends which are closed by plugs 73 u and havedownstream ends which are opened. Note that, in FIG. 3A, the hatchedparts show plugs 73 u. Therefore, the exhaust gas inflow passages 71 iand exhaust gas outflow passages 710 are alternately arranged throughthin partition walls 72. In other words, the exhaust gas inflow passages71 i and exhaust gas outflow passages 710 are comprised of exhaust gasinflow passages 71 i each of which are surrounded by four exhaust gasoutflow passages 710 and of exhaust gas outflow passages 710 each ofwhich are surrounded by four exhaust gas inflow passages 71 i. Inanother embodiment, the exhaust flow passages are comprised of exhaustgas inflow passages with upstream ends and downstream ends which areopened and exhaust gas outflow passages with upstream ends which areclosed by plugs and with downstream ends which are open.

The partition walls 72 are formed from porous materials such ascordierite, silicon carbide, silicon nitride, zirconia, titania,alumina, silica, mullite, lithium aluminum silicate, zirconiumphosphate, and other such ceramics. Therefore, as shown by the arrows inFIG. 3B, the exhaust gas first flows into the exhaust gas inflowpassages 71 i, then passes through the surrounding partition walls 72and flows out to the adjoining exhaust gas outflow passages 710. In thisway, the partition walls 72 form the inner circumferences of the exhaustgas inflow passages 71 i. Note that, the partition walls 72 have averagepore sizes of 10 to 25 μm or so.

The partition walls 72 carry a catalyst which has an oxidation functionat the two side surfaces and the surfaces inside the pores. The catalystwhich has the oxidation function is comprised of palladium Pt, rhodiumRh, palladium Pd, or other such precious metal. In another embodiment,the catalyst which has an oxidation function is comprised of a compositeoxide including cerium Ce, praseodymium Pr, neodymium Nd, lanthanum La,or other such base metal. Further, in another embodiment, the catalystis comprised of a combination of a precious metal and composite oxide.

Now, the exhaust gas contains particulate matter which is formed mainlyfrom solid carbon. This particulate matter is trapped on the particulatefilter 24. In this combustion chamber 2, fuel is burned under an oxygenexcess. Therefore, so long as fuel is not secondarily supplied from thefuel injector 3 and fuel addition valve 27, the particulate filter 24 isin an oxidizing atmosphere. Further, the particulate filter 24 carries acatalyst which has an oxidation function. As a result, the particulatematter which is trapped on the particulate filter 24 is successivelyoxidized. In this regard, if the amount of particulate matter which istrapped per unit time becomes greater than the amount of particulatematter which is oxidized per unit time, the amount of particulate matterwhich is trapped on the particulate filter 24 increases together withthe elapse of the engine operation time.

Therefore, in the embodiment according to the present invention, PMremoval control for removing particulate matter from the particulatefilter 24 is repeatedly performed. As a result, the particulate matteron the particulate filter 24 is removed and the pressure loss of theparticulate filter 24 is decreased.

In the embodiment which is shown in FIG. 1, PM removal control iscomprised of temperature elevation control which raises and holds thetemperature of the particulate filter 24 to the PM removal temperature(for example 600° C.) to remove the particulate matter by oxidation. Toexecute temperature elevation control, in one embodiment, fuel is addedfrom the fuel addition valve 27 and the fuel is burned at the exhaustpassage or particulate filter 24. In another embodiment, fuel isinjected from a fuel injector 3 in the compression stroke or exhauststroke. This fuel is burned in the combustion chamber 2, exhaustpassage, or particulate filter 24.

That is, as shown in FIG. 4, at the time ta1, if the pressure loss ofthe particulate filter 24, that is, the pressure difference PD, becomeslarger than the upper limit value UPD, PM removal control, that is,temperature elevation control, is started. Therefore, the temperature TFof the particulate filter 24 is raised and held up the PM removaltemperature TFPM. As a result, the pressure difference PD becomessmaller. Further, the amount of particulate matter QPM which isdeposited on the particulate filter 24 also becomes smaller. Next, atthe time ta2, if the amount of deposited particulate matter QPM becomessmaller than the lower limit value LQPM, the PM removal control isended. Therefore, the temperature TF of the particulate filter 24 falls.Next, at the time ta3, if the pressure difference PD becomes larger thanthe upper limit value UPD, PM removal control is started. Next, at thetime ta4, if the amount of deposited particulate matter QPM becomessmaller than the lower limit value LQPM, the PM removal control isended. In this way, the PM removal control is repeatedly performed.

The amount of deposited particulate matter QPM, in one embodiment, isexpressed by a counter value obtained by finding the amount of increaseqPMi per unit time and the amount of decrease qPMd per unit time basedon the state of engine operation, and accumulating the totals of theamount of increase qPMi and the amount of decrease qPMd(QPM=QPM+qPMi−qPMd). The amount of increase qPMi, as shown in FIG. 5A,is stored as a function of the fuel injection amount QF and the enginespeed Ne in the form of a map in advance in the ROM 32 (FIG. 1). Thefuel injection amount QF represents the engine load. On the other hand,the amount of decrease qPMd, as shown in FIG. 5B, is stored as afunction of the intake air amount Ga and the temperature TF of theparticulate filter 24 in the form of a map in advance in the ROM 32. Theintake air amount Ga expresses the flow of exhaust gas or oxygen whichflows into the particulate filter 24.

FIG. 6 shows a routine for executing the PM removal control which isshown in FIG. 4. Referring to FIG. 6, at step 101, it is judged if thepressure difference PD of the particulate filter 24 is larger than theupper limit value UPD. When PD>UPD, next, the routine proceeds to step102, where temperature elevation control is performed. That is, thetarget value TTF of the temperature TF of the particulate filter 24 isset to the PM removal temperature TFPM. In the embodiment which is shownin FIG. 1, the temperature of the particulate filter 24 is controlled sothat the actual temperature of the particulate filter 24 becomes thetarget value TTF.

At the next step 103, it is judged if the amount of depositedparticulate matter QPM is smaller than the lower limit value LQPM. WhenQPM≧LQPM, the routine returns to step 102. When QPM<LQPM, the processingcycle is ended. Therefore, the temperature elevation control is ended.At step 101, when PD≦UPD, the processing cycle is ended. In this case,temperature elevation control is not performed.

FIG. 7 shows a routine for calculating the amount of depositedparticulate matter QPM. Referring to

FIG. 7, at step 111, the amount of increase qPMi is calculated from themap of FIG. 5A. At the next step 112, the amount of decrease qPMd iscalculated from the map of FIG. 5B. At the next step 113, the amount ofdeposited particulate matter QPM is calculated (QPM=QPM+qPMi−qPMd).

In another embodiment, the PM removal control is comprised of NOx amountincreasing control for increasing the amount of NOx in the exhaust gaswhich flows into the particulate filter 24, to remove the particulatematter by oxidation by NOx. To increase the amount of NOx, for example,the amount of EGR gas is decreased. In still another embodiment, the PMremoval control is comprised of ozone supply control which suppliesozone to the particulate filter 24 from an ozone supplier which isconnected with the exhaust passage upstream of the particulate filter24, to remove the particulate matter by oxidation by ozone.

In this regard, exhaust gas also contains ash. This ash is also trappedat the particulate filter 24 together with the particulate matter. Thefact that this ash is mainly formed from calcium salts such as calciumsulfate CaSO₄ and calcium zinc phosphate Ca₁₉Zn₂(PO₄)₁₄ was confirmed bythe inventors. The calcium Ca, zinc Zn, phosphorus P, etc. are derivedfrom the engine lubrication oil, while the sulfur S is derived from thefuel. That is, if explaining calcium sulfate CaSO₄ as an example, theengine lubrication oil flows into the combustion chamber 2 and burns.The calcium Ca in the lubrication oil bonds with the sulfur S in thefuel whereby calcium sulfate CaSO₄ is formed.

In this regard, even if PM removal control is performed, the ash is notburned or vaporized. That is, the ash is not removed from theparticulate filter 24 and remains on the particulate filter 24. As aresult, the pressure loss or the pressure difference PD of theparticulate filter 24 increases by the amount of the ash which isdeposited on the particulate filter 24.

That is, if the engine is started from the state of a new particulatefilter 24, as shown in FIG. 8A, the pressure difference PD increasesfrom its initial value PD0, while the amount of deposited particulatematter QPM increases from its initial value zero along the curve CT1.Next, if the pressure difference PD increases from the upper limit valueUPD, PM removal control is started. As a result, as shown in FIG. 8B,the pressure difference PD decreases from the upper limit value UPD,while the amount of deposited particulate matter QPM decreases from thevalue QPM1 along the curve CR1. Next, if the amount of depositedparticulate matter QPM becomes smaller than the lower limit value LQPM,the PM removal control is ended. As a result, as shown in FIG. 8C, thepressure difference PD is increased from the value PD1, while the amountof deposited particulate matter QPM increases from the lower limit valueLQPM along the curve CT2. Next, if the pressure difference PD becomeslarger than the upper limit value UPD, PM removal control is started. Asa result, as shown in FIG. 8D, the pressure difference PD decreases fromthe upper limit value UPD, while the amount of deposited particulatematter QPM decreases from the value QPM2 along the curve CR2. Next, ifthe amount of deposited particulate matter QPM becomes smaller than thelower limit value LQPM, the PM removal control is ended. In this way,the increase and decrease of the pressure difference PD and the amountof deposited particulate matter QPM are alternately repeated.

From a separate viewpoint, FIG. 8A shows a first increasing action ofthe pressure difference PD and the amount of deposited particulatematter QPM, FIG. 8B shows a first decreasing action of the pressuredifference PD and the amount of deposited particulate matter QPM, FIG.8C shows a second increasing action of the pressure difference PD andthe amount of deposited particulate matter QPM, and FIG. 8D shows asecond decreasing action of the pressure difference PD and the amount ofdeposited particulate matter QPM.

In this way, as the engine operation time becomes longer, the amount ofdeposited particulate matter QPM decreases when the increasing action ofthe pressure difference PD and the amount of deposited particulatematter QPM is stopped, that is, when the PM removal control is started(QPM1>QPM2), while the pressure difference PD increases when theincreasing action of the pressure difference PD and the amount ofdeposited particulate matter QPM is started (PD0<PD1<PD2). As a result,the timing of execution of PM removal control is liable to be advancedfrom the optimum timing. In this case, the PM removal processing isunpreferably performed frequently and the amount of fuel consumedunpreferably increases.

On the other hand, generally speaking, the ash which is deposited on theparticulate filter 24 can be considered to be formed from one or both ofthe ash A which deposits in a dispersed manner on the innercircumferences 71 is of the exhaust gas inflow passages 71 i as shown inFIG. 9A, and the ash A which locally deposits at the rear parts orbottom parts 71 ir of the exhaust gas inflow passages 71 i as shown inFIG. 9B. On top of this, the ash A which deposits on the innercircumferences 71 is of the exhaust gas inflow passages 71 i has a largeeffect on the pressure loss or the pressure difference PD of theparticulate filter 24. As opposed to this, the ash A which is depositedat the rear part 71 ir of the exhaust gas inflow passage 71 i has asmall effect on the pressure loss or the pressure difference PD of theparticulate filter 24.

This being so, if the ash A which is deposited on the innercircumferences 71 is is moved to the rear parts 71 ir, the effect of theash on the pressure difference PD is weakened. On this point, there maybe a case where part of the ash A which is deposited on the innercircumferences 71 is is moved to the rear parts 71 ir by the flow of theexhaust gas when the amount of exhaust gas which flows into theparticulate filter 24 is large, like at the time of engine high loadoperation. However, in this case, it is difficult to move a sufficientamount of ash.

Therefore, in the embodiment according to the present invention, amovement promoting control is performed which promotes movement of theash A which is deposited on the inner circumferences 71 is of theexhaust gas inflow passages 71 i to the rear parts 71 ir of the exhaustgas inflow passages 71 i. As a result, the amount of ash which depositson the inner circumferences 71 is of the exhaust gas inflow passages 71i can be decreased and the effect of the ash on the pressure differencePD can be kept small. Therefore, the timing of execution of the PMremoval control can be maintained at the optimum timing.

In the embodiment which is shown in FIG. 1, the movement promotingcontrol is performed by supplying liquid to the particulate filter 24.This liquid is comprised of condensed water which is stored in thecondensed water storage part 14 e.

Further, in the embodiment which is shown in FIG. 1, it is judged if theamount of ash which deposited on the inner circumferences 71 is of theexhaust gas inflow passages 71 i is larger than a predetermined upperlimit amount. When it is judged that the amount of ash which depositedon the inner circumferences 71 is is larger than the upper limit amount,the movement promoting control is performed at the time of engine coldstart. As opposed to this, when it is not judged that the amount of ashwhich deposited on the inner circumferences 71 is is larger than theupper limit amount, the movement promoting control is not performed.This movement promoting control will be explained with reference to FIG.10.

In FIG. 10, the solid line shows the case where the movement promotingcontrol is performed, while the broken line shows the case where themovement promoting control is not performed. Referring to FIG. 10, atthe time tb1, the ignition switch 44 is turned on, the starter switch 45is turned on, and therefore engine startup is started. As a result, theengine speed Ne rises. Next, at the time tb2, the engine speed Neexceeds a predetermined set value NeC (for example 900 rpm) and completeexplosion occurs. Next, in the case where movement promoting control isnot performed, as shown by the broken line in FIG. 10, normal idlingcontrol is performed. That is, when the engine operation is coldoperation, the engine speed Ne is maintained at the cold idling speedNeIC (for example, at the highest, 1000 rpm). Further, the EGR controlvalve 13 is closed, and therefore the feed of EGR gas is prohibited.Next, at the time tb4, when the engine operation is switched to warmoperation, the engine speed Ne is maintained at the warm idling speedNeIW (for example 700 to 800 rpm). Further, the feed of EGR gas isallowed. That is, the opening degree DEGR of the EGR control valve 13 iscontrolled in accordance with the engine operating state. Note that, inthe example which is shown in FIG. 1, when the engine cooling watertemperature and engine lubricating oil temperature are both lower than apredetermined set temperature (for example 20° C.), it is judged thatthe engine operation is cold operation, while when one or both of theengine cooling water temperature and engine lubricating oil temperatureis higher than the set temperature, it is judged that the engineoperation is warm operation.

As opposed to this, when movement promoting control is performed, asshown by the solid line in FIG. 10, after complete explosion at the timetb2, the engine speed Ne is maintained at a predetermined movementpromoting idling speed NeIT (for example, 1500 rpm). This movementpromoting idling speed NeIT is set higher than the normal idling speedsNeIC and NeIW. As a result, the amount of gas which flows through theintake manifold 4, combustion chambers 2, exhaust manifold 5, exhaustpipe 21, and particulate filter 24 is increased. Further, the openingdegree DEGR of the EGR control valve 13 is increased. In the examplewhich is shown in FIG. 10, the opening degree DEGR is made 100%, thatis, the EGR control valve 13 is made full open. At this time, the engineoperation is cold operation, so the bypass control valve 14 d of thecooling device 14 is controlled to the bypass position (FIG. 2). As aresult, a relatively large amount of EGR gas flows through the bypasspassage 14 c. This large amount of EGR gas causes the condensed water tobe discharged from the condensed water storage part 14 e. This condensedwater successively flows together with the EGR gas through the intakemanifold 4, combustion chambers 2, exhaust manifold 5, and exhaust pipe21 and is fed to the inside of the particulate filter 24.

As a result, the ash on the inner circumference 71 is of the exhaust gasinflow passage 71 i is washed away by the condensed water and is movedto the rear part 71 ir. Alternatively, the ash is wet by the condensedwater whereby the ash layer which is formed on the inner circumference71 is of the exhaust gas inflow passage 71 i is destroyed and the asheasily separates from the inner circumference 71 is. The ash whichseparated from the inner circumference 71 is is easily moved by theexhaust gas to the rear part 71 ir during the subsequent engineoperation.

In this case, since the engine operation is cold operation, thecondensed water is fed as a liquid to the particulate filter 24,therefore movement of the ash can be reliably promoted. Note that, dueto the movement promoting control, the amount of condensed water whichpasses through a combustion chamber 2 is relatively small and no waterhammer phenomenon occurs. Further, if movement promoting control isperformed, the particulate matter which is deposited on the innercircumference 71 is also moves to the rear part 71 ir. The particulatematter which was moved in this way is removed by the subsequent

PM removal processing.

Next, if, at the time tb3, a predetermined set time tB has elapsed, thenormal idling control is started. That is, when the engine operation iscold operation, the engine speed Ne is maintained at the cold idlingspeed NeIC and the EGR control valve 13 is closed. Next, if, at the timetb4, the engine operation switches to warm operation, the engine speedNe is maintained at the warm idling speed NeIW and the feed of EGR gasis allowed.

If calling the fuel consumption rate when the particulate filter 24 isnew the “new fuel consumption rate”, according to the inventors, whenthe amount of ash which is deposited on the inner circumferences 71 isof the exhaust gas inflow passages 71 i becomes greater than apredetermined upper limit amount, the amount of increase in the fuelconsumption rate over the new fuel consumption rate is about 13%. Next,the amount of increase in the fuel consumption rate over the new fuelconsumption rate after the movement promoting control is performed isabout 3%. In this way, by the movement promoting control, it is possibleto reliably suppress the increase in the fuel consumption rate.

It is judged if the ash which deposited on the inner circumferences 71is of the exhaust gas inflow passages 71 i is greater than thepredetermined upper limit amount for example as follows. That is, asshown in FIG. 11A, the pressure difference PD and the amount ofdeposited particulate matter QPM change along the curve CT1 at the timeof the first increasing action. The asymptote AST1 of this curve CT1 isrepresented by the following formula:

PD=A1·QPM+(B1+C1)

Further, the pressure difference PD and the amount of depositedparticulate matter QPM change along the curve CR1 at the time of thefirst decreasing action. The asymptote ASR1 of this curve CR1 isrepresented by the following formula:

PD=A1·QPM+B1

The difference of the intercepts of these two formulas is represented byC1. Note that, B1 represents the pressure loss of the particulate filter24 itself and corresponds to PD0.

In the same way, as shown in FIG. 11B, the pressure difference PD andthe amount of deposited particulate matter QPM change along the curveCTi at the time of the i-th increasing action (i=1, 2, . . . ). Theasymptote ASTi of this curve CTi is represented by the followingformula:

PD=Ai·QPM+(Bi+Ci)

Further, the pressure difference PD and the amount of depositedparticulate matter QPM change along the curve CRi at the time of thei-th decreasing action. The asymptote ASRi of this curve CRi isrepresented by the following formula:

PD=Ai·QPM+Bi

The difference of the intercepts of these two formulas is represented byCi.

The difference Ci of the intercepts represents the amount of particulatematter which has deposited on the particulate filter 24 at the time ofthe i-th increasing action of the pressure difference PD and the amountof deposited particulate matter QPM. Alternatively, it represents theamount of particulate matter which is removed from the particulatefilter 24 at the time of the i-th decreasing action of the pressuredifference PD and the amount of deposited particulate matter QPM. Theamount of this particulate matter becomes smaller as the amount of theash which is deposited on the inner circumferences 71 is of the exhaustgas inflow passages 71 i becomes greater. Therefore, as the amount ofthe ash which deposited on inner circumferences 71 is of the exhaust gasinflow passages 71 i increases, the difference Ci or the ratio R(=Ci/C1)becomes smaller. Note that, FIG. 11A shows the case where the differenceCi or the ratio R is large, while FIG. 11B shows the case where thedifference Ci or the ratio R is small.

Therefore, in the embodiment which is shown in FIG. 1, when the ratio Ris smaller than a predetermined lower limit value RL, it is judged thatthe amount of ash which is deposited on the inner circumferences 71 isof the exhaust gas inflow passages 71 i is greater than thepredetermined upper limit amount, while when the ratio R is larger thanthe lower limit value RL, it is judged that the amount of ash which isdeposited on the inner circumference 71 is is smaller than the upperlimit amount.

FIG. 12 shows a routine for executing the engine start control in theembodiment which is shown in FIG. 1. This routine is executed just oncewhen the ignition switch 44 is turned on. Referring to FIG. 12, at thestep 121, the flag X is reset (X=0). This flag X is set (X=1) when thenormal idling control routine (FIG. 14) should be executed and isotherwise reset (X=0). At the next step 122, it is judged if the enginespeed Ne is higher than the set speed NeC. When Ne≦NeC, the routinereturns to step 122. When Ne>NeC, that is, when complete explosionoccurs, next the routine proceeds to step 123 where it is judged if theratio R is smaller than the lower limit value RL. When R<RL, next theroutine proceeds to step 124 where it is judged if the engine operationis cold operation. When the engine operation is cold operation, next theroutine proceeds to step 125 where the movement promoting controlroutine is executed. At the next step 126, the flag X is set (X=1).When, at the step 123, RRL and, at the step 125, the engine operation iswarm operation, the routine proceeds to step 126. Therefore, in thesecases, movement promoting control is not performed.

FIG. 13 shows a routine for executing movement promoting control in theembodiment which is shown in FIG. 1. This routine is for exampleexecuted at step 125 of FIG. 12. Referring to FIG. 13, at step 131, thetarget speed TNe is set to the movement promoting idling speed NeIT. Inthe embodiment which is shown in FIG. 1, the engine speed is controlledso that the actual engine speed becomes the target speed TNe. At thenext step 132, the EGR control valve 13 is opened. At the next step 133,it is judged if the set time tB has elapsed. When the set time tB hasnot elapsed, the routine returns to step 131. When the set time tB haselapsed, the processing cycle is ended. That is, the movement promotingcontrol is ended and the routine proceeds to step 126 of FIG. 12.

FIG. 14 shows the routine for executing the normal idling control.Referring to FIG. 14, step 141, it is judged if the amount of depressionL of the accelerator pedal 39 is zero, that is, if the engine operationis in idling operation. When L>0, that is, when the engine operation isnot idling operation, the processing cycle is ended. When L=0, that is,when the engine operation is idling operation, next the routine proceedsto step 142 where it is judged if the flag X has been set. When the flagX has been reset (X=0), the processing cycle is ended. As opposed tothis, when the flag X has been set (X=1), next the routine proceeds tostep 143. Therefore, from when engine startup is started to when theflag X is set at step 126 of the routine of FIG. 12, the routine doesnot proceed to step 143. At step 143, it is judged if the engineoperation is cold operation. When the engine operation is coldoperation, next the routine proceeds to step 144 where the target speedTNe is set to the cold idling speed NeIC. At the next step 146, the EGRcontrol valve 13 is closed. As opposed to this, when the engineoperation is warm operation, the routine proceeds to step 146 where thetarget speed TNe is set to the warm idling speed NeIW. At the next step147, the feed of EGR gas is allowed.

FIG. 15 shows the routine for calculation of the ratio R. Referring toFIG. 15, at step 151, the pressure difference PD is read. At the nextstep 152, the amount of particulate matter QPM is read. At the next step153, it is judged if the PM removal control has switched from execute tostop. When the PM removal control has not switched from execute to stop,next the routine proceeds to step 154 where it is judged if the PMremoval control has switched from stop to execute. When the PM removalcontrol has switched from stop to execute, the processing cycle isended. When the PM removal control has switched from stop to execute,that is, when the i-th increasing action of the pressure difference PDand the amount of deposited particulate matter QPM ends, the routineproceeds to step 155 where the asymptote ASTi of the curve CTi for thei-th increasing action is determined. Next, when the PM removal controlis switched from execute to stop, that is, when the i-th decreasingaction of the pressure difference PD and the amount of depositedparticulate matter QPM ends, the routine proceeds from step 153 to step156 where the asymptote ASRi of the curve CRi for the i-th decreasingaction is determined. At the next step 157, the difference Ci of theintercepts is calculated. At the next step 158, the ratio R iscalculated (R=Ci/C1). At the next step 159, the parameter “i” isincremented by 1 (i=i+1). Note that, the parameter “i” is set to 1 atthe time of engine startup.

Next, referring to FIG. 16, another embodiment of the ratio R will beexplained. As shown in FIG. 16, the pressure difference PD decreases byDi (=UPD-PD(i+1)) due to the i-th decreasing action. The amount ofdecrease Di or ratio Di/D1 becomes smaller as the amount of ash which isdeposited on the inner circumferences 71 is of the exhaust gas inflowpassages 71 i becomes greater. Therefore, the ratio R is calculated inthe form of Di/D1. In still another embodiment, when the difference Cior the amount of decrease Di is smaller than a predetermined lower limitvalue, it is judged that the amount of ash which is deposited on theinner circumferences 71 is of the exhaust gas inflow passages 71 i isgreater than the predetermined upper limit amount, while when thedifference Ci or the amount of decrease Di is greater than the lowerlimit value, it is judged that the amount of ash which is deposited onthe inner circumference 71 is is smaller than the upper limit amount.

FIG. 17A to FIG. 17C show another embodiment of a condensed waterstorage part 14 e. In the embodiment which is shown in FIG. 17A, thebypass passage 14 c of the cooling device 14 is bent downward. Thecondensed water storage part 14 e is configured by the bent part of thebypass passage 14 c. In the embodiment which is shown in FIG. 17B, thecondensed water storage part 14 e is configured by a recessed part whichis formed at the bottom surface of the intake manifold 4. In theembodiment which is shown in FIG. 17C, the condensed water storage part14 e is configured by a recessed part which is formed at the bottomsurface of the exhaust manifold 5. Note that, in the embodiment which isshown in FIG. 17B and FIG. 17C, the EGR control valve 13 is closed atthe time of movement promoting control. In still another embodiment, acondensed water storage part 14 e is configured by a recessed part whichis formed in the bottom surface of the housing of the exhaustturbocharger 7 or a recessed part which is formed in the bottom surfaceof the exhaust pipe 21.

FIG. 18 shows another embodiment according to the present invention.Referring to FIG. 18, the particulate filter 24 carries a NOx reducingcatalyst 24 a. This NOx reducing catalyst 24 a has the function ofreducing the NOx in the exhaust gas by a reducing agent in an oxidizingatmosphere in which the reducing agent is contained. The NOx reducingcatalyst 24 a is for example comprised of a carrier which is formed fromtitania on which vanadium oxide is carried, that is, a vanadium-titaniacatalyst, or of a carrier which is formed from zeolite on which copperis carried, that is, a copper-zeolite catalyst. In another embodiment,the NOx reducing catalyst is arranged downstream of the particulatefilter 24.

In the exhaust pipe 21 upstream of the NOx reducing catalyst 24 a, areducing agent addition valve 50 is arranged for secondarily adding areducing agent in the exhaust gas. The reducing agent addition valve 50is connected through a reducing agent feed pipe 51 to a reducing agenttank 52. Inside the reducing agent feed pipe 51, a variable dischargepressure-type reducing agent pump 53 is arranged. In the example whichis shown in FIG. 18, the reducing agent is comprised of a urea aqueoussolution. The reducing agent tank 52 stores the urea aqueous solution.

At the time of normal operation after the engine startup has completed,a reducing agent is added from the reducing agent addition valve 50 forreducing the NOx. This reducing agent is next supplied to the NOxreducing catalyst 24 a. As a result, NOx is reduced in the NOx reducingcatalyst 24 a. In this case, the reducing agent is added from thereducing agent addition valve 50 with the NOx reduction additionpressure and the NOx reduction addition time. These NOx reductionaddition pressure and NOx reduction addition time are selected inaccordance with the engine operating state so that the reducing agent,that is, the urea aqueous solution, can be sufficiently atomized.

In the embodiment which is shown in FIG. 18, the liquid which issupplied in the movement promoting control is comprised of a reducingagent which is added from the reducing agent addition valve 50, that is,a urea aqueous solution. That is, as shown in FIG. 19, after enginestartup at the time tc1, if complete explosion occurs at the time tc2,the engine speed Ne is maintained at the movement promoting idling speedNeIT. As a result, the amount of exhaust gas which runs through theparticulate filter 24 is increased. At this time, the reducing agent isadded from the reducing agent addition valve 50 with the movementpromoting addition pressure in the form of a liquid. This liquidreducing agent is supplied by the exhaust gas to the particulate filter24. As a result, movement of the ash on the inner circumferences 71 isof the exhaust gas inflow passages 71 i to the rear parts 71 r ispromoted. Next, if, at the time tc3, a movement promoting addition timetC has elapsed, the normal idling control is started. Further, additionof the liquid reducing agent is stopped. That is, the movement promotingcontrol is stopped.

The movement promoting addition pressure and the movement promotingaddition time are set so that the reducing agent is not atomized much atall and is supplied in the form of a liquid to the particulate filter24. That is, the reducing agent is added with a movement promotingaddition pressure which is lower than the NOx reduction additionpressure or with a movement promoting addition time which is longer thanthe NOx reduction addition time. Note that, the movement promotingaddition pressure and the movement promoting addition time are set inaccordance with the engine operating state. In the embodiment which isshown in FIG. 18, the movement promoting addition pressure becomeshigher as the intake air amount becomes greater and becomes higher asthe temperature of the exhaust gas which flows into the particulatefilter 24 becomes higher. Further, the movement promoting addition timebecomes longer as the pressure inside the exhaust pipe 21 becomes higherand becomes longer the greater the amount of ash which is deposited onthe inner circumferences 71 is of the exhaust gas inflow passages 71 i.

FIG. 20 shows a routine for executing the movement promoting controlwhich is shown in FIG. 19.

This routine is for example executed at step 125 of FIG. 12. Referringto FIG. 19, at step 161, the target speed TNe is set at the movementpromoting idling speed NeIT. At the next step 162, the movementpromoting addition pressure is calculated. At the next step 163, themovement promoting addition time is calculated. At the next step 164,the reducing agent is added from the reducing agent addition valve 50with the movement promoting addition pressure for the movement promotingaddition time. Next, the processing cycle is ended. That is, themovement promoting control is ended, and the routine proceeds to step126 of FIG. 12.

Next, another embodiment of the movement promoting control in theembodiment which is shown in FIG. 1 or FIG. 18 will be explained. Inthis embodiment, the liquid which is supplied to the movement promotingcontrol is comprised of fuel which is added from the fuel addition valve27. The fuel which is added from the fuel addition valve 27 is used forreducing the NOx at the catalyst which is carried on the particulatefilter 24. Alternatively, it is used for the above-mentioned temperatureelevation control.

When the movement promoting control must be performed, liquid fuel isadded from the fuel addition valve 27. In this case, the fuel is addedwith an addition pressure which is lower than the addition pressure forNOx reduction or temperature elevation control or an addition time whichis longer than the addition time for NOx reduction or temperatureelevation control. As a result, the fuel is added in the form of aliquid to the particulate filter 24.

If, in this way, liquid is added from the reducing agent addition valve50 (FIG. 18) or fuel addition valve 27 (FIG. 1) for movement promotingcontrol, an additional configuration is not required.

FIG. 21 shows still another embodiment according to the presentinvention. Referring to FIG. 21, a liquid addition valve 55 is arrangedin the EGR passage 12 to secondarily add liquid into the EGR gas. Theliquid addition valve 55 is connected through a liquid feed pipe 56 to aliquid tank 57. Inside the liquid feed pipe 56, a variable dischargeliquid pump 58 is arranged. In the example which is shown in FIG. 21,the liquid is comprised of water. The water is stored in the liquid tank57. In another embodiment, the liquid is comprised of an aqueoussolution or liquid fuel.

In the embodiment which is shown in FIG. 21, the liquid which issupplied in the movement promoting control is comprised of the liquidwhich is added from the liquid addition valve 55, that is, water. Thatis, as shown in FIG. 22, if, after engine startup at the time td1,complete explosion occurs at the time td2, the engine speed Ne ismaintained at the movement promoting idling speed NeIT. Further, the EGRcontrol valve 13 is opened. At this time, water is added from the liquidaddition valve 55 with the movement promoting addition pressure. Thiswater is supplied by the exhaust gas to the particulate filter 24. As aresult, movement of the ash on the inner circumferences 71 is of theexhaust gas inflow passages 71 i to the rear parts 71 r is promoted. Inthis case, the movement promoting addition pressure and the movementpromoting addition time are set so that the water is supplied in theform of a liquid to the particulate filter 24. Next, if, at the timetd3, a movement promoting addition time tD elapses, the normal idlingcontrol is started. Further, the addition of water is stopped. That is,the movement promoting control is stopped.

FIG. 23 shows a routine for executing the movement promoting controlwhich is shown in FIG. 22. This routine is for example executed at step125 of FIG. 12. Referring to FIG. 23, at step 171, the target speed TNeis set to the movement promoting idling speed NeIT. At the next step172, the EGR control valve 13 is opened. At the next step 173, themovement promoting addition pressure is calculated. At the next step174, the movement promoting addition time is calculated. At the nextstep 175, liquid is added from the liquid addition valve 55 with themovement promoting addition pressure for the movement promoting additiontime. Next, the processing cycle is ended. That is, the movementpromoting control is ended and the routine proceeds to step 126 of FIG.12.

In the embodiment which is shown in FIG. 24A, a liquid addition valve 55is arranged at the intake duct 6. In the embodiment which is shown inFIG. 24B, the liquid addition valve 55 is arranged at the exhaustmanifold 5. In the embodiment which is shown in FIG. 24C, the liquidaddition valve 55 is arranged at the exhaust pipe 21. Note that, in theembodiments which are shown from FIG. 24A to FIG. 24C, the EGR controlvalve 13 is closed at the time of movement promoting control.

FIG. 25 shows still another embodiment according to the presentinvention. Referring to FIG. 25, an exhaust control valve 60 which canopen and close the exhaust pipe 23 is arranged in the exhaust pipe 23downstream of the particulate filter 24. The exhaust control valve 60 isnormally set full open.

In the embodiment which is shown in FIG. 25, the movement promotingcontrol is comprised of generation of pressure pulsation in theparticulate filter 24. That is, as shown in FIG. 26, if, after enginestartup at the time te1, complete explosion occurs at the time te2, theengine speed Ne is maintained at the movement promoting idling speedNeIT. At this time, the exhaust control valve 60 is alternatelyrepeatedly opened and closed. As a result, pulsation occurs in thepressure in the particulate filter 24. Due to this pressure pulsation,the ash layer which is formed at the inner circumferences 71 is of theexhaust gas inflow passages 71 i is destroyed and the ash easily peelsoff from the inner circumferences 71 is. The ash which peeled off fromthe inner circumferences 71 is is easily moved by the exhaust gas to therear parts 71 ir during the subsequent engine operation. Next, if, atthe time tea, a predetermined set time tE has elapsed, the normal idlingcontrol is started. Further, the exhaust control valve 60 is maintainedfull open. That is, the movement promoting control is stopped.

FIG. 27 shows the routine for executing the movement promoting controlwhich is shown in FIG. 26. This routine is for example executed at step125 of FIG. 12. Referring to FIG. 27, at step 181, the target speed TNeis set to the movement promoting idling speed NeIT. At the next step182, the exhaust control valve 60 is opened and closed repeatedly. Atthe next step 183, it is judged if the set time tE has elapsed. When theset time tE has not elapsed, the routine returns to step 181. When theset time tE has elapsed, the processing cycle is ended. That is, themovement promoting control is stopped and the routine proceeds to step126 of FIG. 12.

FIG. 28 shows still another embodiment according to the presentinvention. Referring to FIG. 28, the catalytic converter 22 has avibrator 61 attached to it.

In the embodiment which is shown in FIG. 28, the movement promotingcontrol is comprised of the generation of vibration at the particulatefilter 24.

That is, as shown in FIG. 29, after engine startup at the time tf1, ifcomplete explosion occurs at the time tf2, the engine speed Ne ismaintained at the movement promoting idling speed NeIT. At this time,the vibrator 61 is actuated. As a result, the particulate filter 24 isgiven vibration. Due to this vibration, the ash layer which is formed atthe inner circumferences 71 is of the exhaust gas inflow passages 71 iis destroyed and the ash is easily separated from the innercircumferences 71 is. The ash which is separated from the innercircumferences 71 is is easily moved by the exhaust gas to the rearparts 71 ir during the subsequent engine operation. Next, if, at thetime tf3, a predetermined set time tF elapses, the normal idling controlis started. Further, the vibrator 61 is stopped. That is, the movementpromoting control is stopped.

FIG. 30 shows the routine for executing the movement promoting controlwhich is shown in FIG. 29. This routine is for example executed at step126 of FIG. 12. Referring to FIG. 30, at step 191, the target speed TNeis set to the movement promoting idling speed NeIT. At the next step192, the vibrator 61 is actuated. At the next step 193, it is judged ifthe set time tF has elapsed. When the set time tF has not elapsed, theroutine returns to step 191. When the set time tF has elapsed, theprocessing cycle is ended. That is, the movement promoting control isstopped and the routine proceeds to step 126 of FIG. 12.

FIG. 31 shows still another embodiment of the present invention. In themovement promoting control of the embodiment which is shown in FIG. 31,first, temperature elevation control for movement promotion is performedwhere the temperature TF of the particulate filter 24 rises to themovement promoting temperature TFT which is higher than the PM removalcontrol. Next, exhaust gas amount increasing control is performed totemporarily make the amount of exhaust gas which runs through theparticulate filter 24 increase. As a result, the ash shrinks due to theheating, the ash layer which is formed on the inner circumferences 71 isof the exhaust gas inflow passages 71 i is destroyed, and the ash easilypeels off from the inner circumferences 71 is. The ash which peeled offfrom the inner circumferences 71 is is easily and reliably moved by theincreased exhaust gas to the rear parts 71 ir. Note that, the movementpromoting temperature TFT is for example from 630° C. to 1100° C. or so.

The movement promoting control of this embodiment is performed at thetime of normal operation after engine startup has been completed. Thatis, as shown in FIG. 31, at the time tg1, PM removal control is started,whereby the temperature TF of the particulate filter 24 is raised to thePM removal temperature TFPM.

Next, at the time tg2, the amount of deposited particulate matter QPMbecomes smaller than the lower limit value LQPM and the PM removalcontrol is ended. Following the PM removal control, movement promotingcontrol is started. Specifically, first, temperature elevation controlfor movement promotion is started. That is, the temperature TF of theparticulate filter 24 is raised from the PM removal temperature TFPM tothe movement promoting temperature TFT and held there. If doing this,the energy which is required for the temperature elevation control formovement promotion can be decreased. Next, if, at the time tg3, apredetermined set time tG1 elapses, the temperature elevation controlfor movement promotion is ended. Next, exhaust gas amount increasingcontrol is started. As a result, the amount of exhaust gas QEX whichflows through the particulate filter 24 is increased. Next, if, at thetime tg4, a predetermined set time tG2 has elapsed, the exhaust gasamount increasing control is ended. Therefore, the movement promotingcontrol is ended.

Note that, to execute the temperature elevation control for movementpromotion, in one embodiment, fuel is added from the fuel addition valve27. This fuel is burned in the exhaust passage or particulate filter 24.In another embodiment, fuel is injected from a fuel injector 3 in thecompression stroke or the exhaust stroke and this fuel is burned in thecombustion chamber 2, exhaust passage, or particulate filter 24. On theother hand, to execute exhaust gas amount increasing control, the enginespeed or the throttle opening degree is increased.

FIG. 32 shows a routine for executing the exhaust purification controlwhich is shown in FIG. 31. Referring to FIG. 32, at step 201, the PMremoval control routine which is shown in FIG. 6 is executed. At thenext step 202, it is judged if the ratio R is smaller than the lowerlimit value RL. When R<RL, next the routine proceeds to step 203 wherethe movement promoting control routine is executed. As opposed to this,when RRL, the processing cycle is ended. Therefore, in this case, themovement promoting control routine is not executed.

FIG. 33 shows a routine for executing the movement promoting controlwhich is shown in FIG. 31. This routine is for example executed at step203 of FIG. 32. Referring to FIG. 33, at step 211, the target value TTFof the temperature TF of the particulate filter 24 is set to themovement promoting temperature TFT. At the next step 212, it is judgedwhether the set time tG1 has elapsed. When the set time tG1 has notelapsed, the routine returns to step 211. When the set time tG1 haselapsed, next the routine proceeds to step 213 where exhaust gas amountincreasing control is performed. At the next step 214, it is judged ifthe set time tG2 has elapsed. When the set time tG2 has not elapsed, theroutine returns to step 213. When the set time tG2 has elapsed, theprocessing cycle is ended. That is, exhaust gas amount increasingcontrol ends, therefore the movement promoting control is ended.

In another embodiment, the exhaust gas amount increasing control isomitted. In this case, the ash which is peeled off from the innercircumferences 71 is by the temperature elevation control for movementpromotion is easily moved to the rear parts 71 ir by the exhaust gasduring the subsequent engine operation.

FIG. 34 shows another embodiment of the movement promoting control inthe embodiment which is shown in FIG. 24C. In the embodiment which isshown in FIG. 34, the movement promoting control is comprised ofmovement promoting control during stop which is performed when theengine is stopped and movement promoting control during start which isperformed when the engine is subsequently started.

That is, as shown in FIG. 34, if, at the time th1, the ignition switch44 is turned off, the engine operation is stopped. As a result, theengine speed Ne falls to zero. Next, if a predetermined set time tH1elapses, movement promoting control during stop is performed. That is,liquid is added from the liquid addition valve 55 with the movementpromoting addition pressure. As a result, ash on the innercircumferences 71 is of the exhaust gas inflow passages 71 i is washedaway by the condensed water and moved to the rear parts 71 ir.Alternatively, the ash is wet by the condensed water, the ash layerwhich is formed at the inner circumferences 71 is of the exhaust gasinflow passages 71 i is destroyed, and the ash easily peels off from theinner circumferences 71 is. Note that, the set time tH1 is set to thetime necessary for lowering the temperature TF of the particulate filter24 so that the liquid which is added from the liquid addition valve 55does not vaporize at the particulate filter 24. Next, if, at the timeth3, liquid is added for the movement promoting addition time tH2, theaddition of liquid is stopped. That is, movement promoting controlduring stop is stopped.

Next, at the time th4, the ignition switch 44 is turned on and theengine is started. Next, if, at the time th5, complete explosion occurs,movement promoting control during start is started. That is, the enginespeed Ne is maintained at the movement promoting idling speed NeIT. As aresult, the amount of exhaust gas which runs through the particulatefilter 24 is increased.

Therefore, ash which peels off from the inner circumferences 71 is ofthe exhaust gas inflow passages 71 i is easily moved to the rear parts71 ir. Next, if, at the time th6, a predetermined set time tH3 haselapsed, the normal idling control is started. That is, the movementpromoting control during start is stopped.

FIG. 35 shows a routine for executing the engine stop control which isshown in FIG. 34. This routine is executed just once when the ignitionswitch 44 is turned off. Referring to FIG. 35, at step 221, the flag XXis reset (XX=0). This flag XX is set (XX=1) when movement promotingcontrol during start should be executed and is otherwise reset (XX=0).At the next step 222, the engine operation is stopped. At the next step223, it is judged if the ratio R is smaller than the lower limit valueRL. When R<RL, next the routine proceeds to step 224 where the movementpromoting control routine during stop is executed. At the next step 225,the flag XX is set (XX=1). At the next step 226, the powering of theelectronic control unit 30 is stopped. Next, the processing cycle isended. As opposed to this, when R≧RL, the routine proceeds from step 223to step 226. Therefore, in this case, movement promoting control is notperformed.

FIG. 36 shows a routine for executing the engine start control which isshown in FIG. 34. This routine is executed one time when the ignitionswitch 44 is turned on. Referring to FIG. 36, at step 231, the flag Xwhich was explained referring to FIG. 12 is reset (X=0). At the nextstep 232, it is judged if the engine speed Ne is higher than a set speedNeC. When NeNeC, the routine returns to step 232. When Ne>NeC, that is,when complete explosion occurs, next the routine proceeds to step 233where it is judged if the flag XX explained with reference to FIG. 35 isset. When the flag XX is set (XX=1), next the routine proceeds to step234 where the movement promoting control routine during start isexecuted. At the next step 235, the flag X is set (X=1). When, at step233, the flag XX is reset (XX=0), the routine proceeds to step 235.Therefore, in this case, movement promoting control during start is notperformed.

FIG. 37 shows the routine for executing the movement promoting controlduring stop which is shown in FIG. 34. This routine is for exampleexecuted at step 224 of FIG. 35. Referring to FIG. 37, at step 241, itis judged if the set time tH1 has elapsed from when the ignition switch44 was turned off. When the set time tH1 has not elapsed, the routinereturns to step 241. When the set time tH1 has elapsed, next the routineproceeds to step 242 where the movement promoting addition pressure iscalculated. At the next step 243, the movement promoting addition timeis calculated. At the next step 244, the liquid is added from the liquidaddition valve 55 with the movement promoting addition pressure for themovement promoting addition time. Next, the processing cycle is ended.That is, the movement promoting control during stop is ended and theroutine proceeds to step 225 of FIG. 35.

FIG. 38 shows a routine for execution of movement promoting controlduring start which is shown in FIG. 34. This routine is for exampleexecuted at step 234 of FIG. 36. Referring to FIG. 38, at step 251, thetarget speed TNe is set to the movement promoting idling speed NeIT. Atthe next step 252, it is judged if the set time tH3 has elapsed. If theset time tH3 has not elapsed, the routine returns to step 251. When theset time tH3 has elapsed, the processing cycle is ended. That is, themovement promoting control during start is stopped and the routineproceeds to step 235 of FIG. 36.

FIG. 39 shows still another embodiment according to the presentinvention. The embodiment which is shown in FIG. 39 differs from theembodiment which is shown in FIG. 34 in the point that the catalyticconverter 24 has a cooler 62 attached to it and the liquid which isadded to the particulate filter 24 is solidified by the cooler 62.

That is, as shown in FIG. 40, if, at the time tj1, the ignition switch44 is turned off, the engine operation is stopped, then a predeterminedset time tJ1 elapses, movement promoting control during stop isperformed. That is, liquid is added from the liquid addition valve 55with the movement promoting addition pressure. As a result, the ash onthe inner circumferences 71 is of the exhaust gas, inflow passages 71 iis washed away by the condensed water and is moved to the rear parts 71ir. Alternatively, the ash is wet by condensed water, the ash layerwhich is formed on the inner circumferences 71 is of the exhaust gasinflow passages 71 i is destroyed, and the ash easily separates from theinner circumferences 71 is. Note that, the set time tJ1 is set in thesame way as the above set time tH1.

Next, if, at the time tj3, the liquid is added for a movement promotingaddition time tJ2, the addition of the liquid is stopped. Next, if, attj4, a predetermined set time tJ3 elapses from the stopping of liquidaddition, the cooler 62 is actuated and the liquid which is added to theparticulate filter 24 solidifies. As a result, the liquid expands, sothe ash layer which is formed on the inner circumferences 71 is of theexhaust gas inflow passages 71 i is further destroyed. Therefore, theash is further easily peeled off from the inner circumferences 71 is.Next, at the time tj5, if a predetermined set time tJ4 elapses, thecooler 62 is stopped. That is, the movement promoting control duringstop is stopped. Note that, the set time tJ4 is set to the time which isrequired for the liquid which was added to the particulate filter 24 tosufficiently solidify.

Next, at the time tj6, the ignition switch 44 is turned on and theengine is started. At this time, the solidified liquid melts. Next, atthe time tj7, if complete explosion occurs, movement promoting controlduring start is started. That is, the engine speed Ne is maintained atthe movement promoting idling speed NeIT. As a result, the amount ofexhaust gas which flows through the inside of the particulate filter 24is increased. Therefore, the ash which is separated from the innercircumferences 71 of the exhaust gas inflow passages 71 i is easilymoved to the rear parts 71 ir. Next, at the time tj8, when apredetermined set time tJ5 has elapsed, the normal idling control isstarted. That is, the movement promoting control during start isstopped.

FIG. 41 shows the routine for execution of the movement promotingcontrol during stop which is shown in FIG. 39. This routine is forexample executed at step 224 of FIG. 35. Referring to FIG. 41, at step261, it is judged if the set time tJ1 has elapsed from when the ignitionswitch 44 was turned off. When the set time tJ1 has not elapsed, theroutine returns to step 261. When the set time tJ1 has elapsed, next theroutine proceeds to step 262, where the movement promoting additionpressure is calculated. At the next step 263, the movement promotingaddition time is calculated. At the next step 264, the liquid is addedfrom the liquid addition valve 55 with the movement promoting additionpressure for the movement promoting addition time. At the next step 265,it is judged if the set time tJ3 has elapsed from when addition of theliquid was stopped. When the set time tJ3 has not elapsed, the routinereturns to step 265. When the set time tJ3 has elapsed, next the routineproceeds to step 266 where the cooler 62 is actuated. At the next step267, it is judged if the set time tJ4 has elapsed from when the cooler63 was actuated. When the set time tJ4 has not elapsed, the routinereturns to step 266. When the set time tJ4 has elapsed, next theprocessing cycle is ended. That is, the movement promoting controlduring stop is ended, and the routine proceeds to step 225 of FIG. 35.

Note that, in the embodiment which is shown in FIG. 34, there may be acase where the atmospheric temperature becomes considerably low whilethe engine operation is stopped and the liquid which is added to theparticulate filter 24 solidifies. In this case as well, the ash layerwhich is formed on the inner circumferences 71 is of the exhaust gasinflow passages 71 i is further destroyed, whereby the ash easily ismoved to the rear parts 71 ir.

REFERENCE SIGNS LIST

-   1 engine body-   12 EGR passage-   14 e condensed water storage part-   21 exhaust pipe-   24 particulate filter-   26 pressure difference sensor-   71 i exhaust gas inflow passage-   71 o exhaust gas outflow passage-   72 partition wall

1. An exhaust purification system comprising: an internal combustionengine; an engine exhaust passage; a particulate filter configured totrap particulate matter contained in exhaust gas, the particulate filterbeing disposed inside the engine exhaust passage, the particulate filterincluding exhaust gas inflow passages and exhaust gas outflow passages,and the exhaust pas inflow passages and the exhaust gas outflow passagesbeing alternately arranged through porous partition walls; a detectingmeans for detecting pressure loss of the particulate filter; a movementpromoting means for promoting movement of ash deposited on innercircumferences of the exhaust gas inflow passages to rear parts of theexhaust gas inflow passages; and a PM removing means for performing PMremoval control for removing the particulate matter from the particulatefilter when the detected pressure loss is greater than a predeterminedupper limit value, wherein the movement promoting means determineswhether an mount of ash deposited on the inner circumferences of theexhaust gas inflow passages is greater than a predetermined upper limitamount, and the movement promoting means performs movement promotingcontrol when the movement promoting means determines that the amount ofash is greater than the predetermined upper limit amount.
 2. (canceled)3. The exhaust purification system according to claim 1, wherein themovement promoting means supplies a liquid to the particulate filter, toperform the movement promoting control.
 4. The exhaust purificationsystem according to claim 3, wherein the liquid is comprised of at leastone of water, an aqueous solution, or a liquid fuel.
 5. The exhaustpurification system according to claim 3, further comprising: acondensed water storage part disposed in at least one of an engineintake passage, the engine exhaust passage upstream of the particulatefilter, or an exhaust gas recirculation passage that connects the engineintake passage and the engine exhaust passage with each other, thecondensed water storage part being configured to store condensed watergenerated at the internal combustion engine, wherein the movementpromoting means supplies the condensed water stored in the condensedwater storage part to the particulate filter, to perform the movementpromoting control.
 6. The exhaust purification system according to claim3, further comprising: a NOx reducing catalyst arranged inside theparticulate filter or in the engine exhaust passage downstream of theparticulate filter; a reducing agent addition valve configured tosecondarily add a liquid reducing agent into the engine exhaust passageupstream of the particulate filter; and a NOx reducing means for addinga liquid reducing agent from the reducing agent addition valve with aNOx reduction addition pressure and a NOx reduction addition time forreducing the NOx, wherein the movement promoting means adds the liquidreducing agent from the reducing agent addition valve with an additionpressure that is lower than the NOx reduction addition pressure or withan addition time that is longer than the NOx reduction addition time, toperform the movement promoting control.
 7. The exhaust purificationsystem according to claim 1, wherein the movement promoting means makespressure inside of the particulate filter pulsate, to perform themovement promoting control.
 8. The exhaust purification system accordingto claim 1, wherein the movement promoting means makes the particulatefilter vibrate, to perform the movement promoting control.
 9. Theexhaust purification system according to claim 1, wherein the movementpromoting means makes temperature of the particulate filter rise to atemperature higher than that at the time of the PM removal control, toperform the movement promoting control.
 10. The exhaust purificationsystem according to claim 1, wherein the movement promoting means feedsa liquid to the particulate filter, and the movement promoting meansmakes the liquid solidify, to perform the movement promoting control.11. An exhaust purification system comprising: an internal combustionengine; an engine exhaust passage; a particulate filter configured totrap particulate matter contained in exhaust gas, the particulate filterbeing disposed inside the engine exhaust passage, the particulate filterincluding exhaust gas inflow passages and exhaust gas outflow passages,and the exhaust gas inflow passages and the exhaust gas outflow passagesbeing alternately arranged through porous partition walls; a pressureloss sensor configured to detect pressure loss of the particulatefilter; an electronic control unit configured to: (i) promote movementof ash deposited on inner circumferences of the exhaust gas inflowpassages to rear parts of the exhaust gas inflow passages, (ii) performPM removal control for removing the particulate matter from theparticulate filter when the detected pressure loss is greater than apredetermined upper limit value, (iii) determine whether an amount ofash deposited on the inner circumferences of the exhaust gas inflowpassages is greater than a predetermined upper limit mount, and (iv)perform movement promoting control when the electronic control unitdetermines that the amount of ash is greater than the predeterminedupper limit amount.
 12. An exhaust purification method for a vehicleincluding: an internal combustion engine; an engine exhaust passage; aparticulate filter configured to trap particulate matter contained inexhaust gas, the particulate filter being disposed inside the engineexhaust passage, the particulate filter including exhaust gas inflowpassages and exhaust gas outflow passages, and the exhaust gas inflowpassages and the exhaust gas outflow passages being alternately arrangedthrough porous partition walls; and a pressure loss sensor configured todetect pressure loss of the particulate filter; an electronic controlunit, the exhaust purification method comprising: (i) promoting, by theelectronic control unit, movement of ash deposited on innercircumferences of the exhaust gas inflow passages to rear parts of theexhaust gas inflow passages; (ii) performing, by the electronic controlunit, PM removal control for removing the particulate matter from theparticulate filter when the detected pressure loss is greater than apredetermined upper limit value; (iii) determining, by the electroniccontrol unit, whether an amount of ash deposited on the innercircumferences of the exhaust gas inflow passages is greater than apredetermined upper limit amount; and (iv) performing, by the electroniccontrol unit, movement promoting control when the electronic controlunit determines that the amount of ash is greater than the predeterminedupper limit amount.